Cryptography is used to hide information. One facet of modern cryptography in computer science utilizes block ciphers to encrypt plaintext. A block cipher operates on blocks of fixed length, often 64 or 128 bits. Because messages may be of any length, and because encrypting the same plaintext under the same key always produces the same output, several modes of operation have been utilized that allow block ciphers to provide confidentiality for messages of arbitrary length.
One of the modes of operation for block ciphers is known as classic output feedback mode (OFB). OFB effectively transforms a block cipher into a synchronous stream cipher. The block cipher is set up to generate a stream of pseudo random bits by iteratively enciphering a block using the output of the previous cycle as the input of the current cycle. Another way to describe OFB is that it generates keystream blocks, which are then XORed with plaintext blocks to create the ciphertext. Because of the symmetry of the XOR operation, encryption and decryption with OFB are exactly the same.
One concern with OFB is that is has a maximum cycle length of 2 to the power of the block size (in bits). As a result, this can be a major concern for encryption with small block sizes. The integrity and confidentiality of the message may be comprised in some cases. Therefore, a mechanism to increase the state size and extend the cycle length using OFB mode would be beneficial.